What are C3 and C4 Native Grass?

The perennial grasses can be classified as either C3 or C4 plants. These  terms refer to the different pathways that plants use to capture carbon dioxide during photosynthesis. All species have the more primitive C3 pathway, but the  additional C4 pathway evolved in species in the wet and dry  tropics. The first product of carbon fixation in C3 plants involves a 3-carbon molecule, whilst C4 plants initially produce a 4-carbon molecule that then enters the C3 cycle. Why are these differences important?

These differences are important because the two  pathways are also associated with different growth requirements.  C3 plants are adapted to cool season establishment and growth in either wet or dry environments.   On the other hand, C4 plants are more adapted to warm or hot seasonal conditions under moist or dry environments.  A feature of C3 grasses is their greater tolerance of frost compared to C4 grasses.  C3 species also tend to generate less bulk than C4 species; however, feed quality is often higher than C4 grasses.  Differences between C3 and C4 species are shown in Table 1.

Table 1:  Features of C3 and C4 grasses

 

C3

C4

Initial    molecule formed during photosynthesis

3 carbon

4 carbon

Growth    period

Cool season or yearlong

Warm season

Light requirements

Lower

Higher

Temperature    requirements

Lower

Higher

Moisture    requirements

Higher

Lower

Frost    sensitivity

Lower

Higher

Feed    quality

Higher

Lower

Production

Lower

Higher

Examples

weeping grass and common wheatgrass

kangaroo grass, red grass and wire grass

The presence of both C3 and C4 species can be desirable in a pasture as they can occupy different niches (e.g. C3 species are often more abundant in the shade of trees and on southerly aspects, while C4 species often dominate full-sun conditions and northerly aspects) and thereby provide greater groundcover across a range of conditions.  It is not uncommon to find both C3 and C4 species in one paddock.  This has advantages in providing a broader spread of production throughout the year for both grazing enterprises and native animals.